Theoretical prediction of pressure-stabilized all-nitrogen N12 molecular crystals with π–π stacking

Abstract

All-nitrogen compounds are ideal high-energy-density materials as they decompose into environmentally friendly nitrogen gas (N₂). However, achieving structural stability often conflicts with high-energy performance. In this study, we demonstrated that two aromatic pentazole rings can be linked via an –NN– bond with sp² orbital hybridization, resulting in a planar π-conjugated compound known as N₁₂. Computational analyses, including the electron localization function and isochemical shielding surface calculations, demonstrated that the pentazole anion in N₁₂ maintained electron delocalization and exhibited aromaticity. Interestingly, under high pressure, the N₁₂ molecule formed a super π–π stacking crystalline structure. The thermodynamic and dynamic stabilities of crystalline N₁₂ were verified using phonon spectrum and ab initio molecular dynamics calculations. Electronic structure calculations revealed that the N₁₂ crystal exhibited semiconducting properties with a large bandgap and was comparable to stable CHON energetic materials. Unlike other all-nitrogen compounds, π–π stacking in the N₁₂ crystalline structure contributed to a high mass density and resulted in a large decomposition barrier, which was crucial for achieving high energy performance and high structural stability. Therefore, further evaluations of detonation performance revealed that the N₁₂ crystalline possessed excellent detonation velocity and pressure among the known all-nitrogen molecular crystals. This work enhances the understanding of nitrogen chemistry and provides new insights into the stabilization of all-nitrogen compounds through π–π stacking.